At the present time counter-rotating airscrews are designed to operate as separate, distinct units with a space between them, either one just in front of the other or one above the other. This present arrangement depends on the lift from each set of blades acting independently to power the helicopters or propeller driven aircraft. None of the previously issued patents attempt to use counter-rotating blades for the expressed sole purpose of using the passing velocities combined to accelerate the velocity of the airstream over the primary lift airfoil to increase lift. None of them use a non-lift plurality of blades whose sole purpose is the acceleration of the airstream over the upper surface of the lower set of primary airfoils.
Fry, U.S. Pat. No. 3,835,332 uses counter-rotators acting as independent units with a ring attached to the upper blades 10. Neither set of blades contributes to the velocity of the airstream passing over the upper surface of each independent airfoil. The vertical sides of the ring 12 would create unnecessary drag and impede the velocity of the helicopter which basically moves in a "horizontal free-fall." Neither Fry, U.S. Pat. No. 3,870,847 or MacIntosh, U.S. Pat. No. 1,056,288 use a ring with venturi properties to accelerate airflow for airplane propeller use. Sudrow, U.S. Pat. No. 3,127,093 shows his counter-rotating ring supported by four struts 18, that create drag. His ring 12 would create this drag during the horizontal flight of the helicopter. His counter-rotating blades do not add increased velocity to the airstream passing over the upper surface of any blades.
Anderson, U.S. Pat. No. 3,424,135 is not an adequate solution. The blades which intersect each other at their trailing edges would destroy the impetus of the airstream flowing across the upper surface of the airfoil where its own inertia carries it down past the trailing edge. The reactive energy of this downward effect would be lost to the airfoil.
Velkoff, U.S. Pat. No. 3,695,780 does not use a counter-rotator in any form. His main concern is with increasing the strength of the blades.